The present invention relates to an optical recording disc used for optically recording and reproducing information.
There is known a so-called double-face optical recording disc comprising two disc bases having recording layers on the surfaces thereof, respectively, bonded to each other oppositely by the medium of an adhesive layer. This double-face optical recording disc has an advantage for a large recording capacity.
Conventionally, this double-face optical recording disc is prepared by coating its respective disc base surfaces to be bonded to each other, using a roller coating method, with a pure solid hot melt adhesive such as an adhesive mainly containing EVA resin excluding any liquid or solvent. Also a reactive adhesive such as epoxy resin type adhesive is used therefor in some cases.
This conventional type double-face disc has, however, some manufactural problems. One problem is that, when the disc bases thereof are made of glass and coated with the hot melt adhesive, using the roller coating method as described above, the surfaces of the glass bases cannot be entirely and sufficiently coated with the hot melt adhesive, that is, the surfaces to be bonded to each other cannot be uniformly bonded together.
Another problem is that, when a reactive adhesive such as one mainly containing epoxy resin is used for bonding two disk bases, it takes a long period of time for the adhesive layer to be completely hardened, which results in low productivity thereof.
It is conceivable that a so-called 2P-adhesive (photo-polymerization adhesive) having ultraviolet-ray hardenability is used for bonding two disc bases together. However, there lies also a problem that, since a so-called double-face optical disc comprises two disc bases, both of which are provided with a recording layer, respectively, not permitting light to penetrate therethrough, the adhesive between such recording layers cannot be irradiated by ultraviolet rays, with the result that the adhesive cannot be hardened all over the inner surfaces of the disc bases.